Acoustical diaphragm



June 13, 1933. w. c. s'rENGl-:R 1,913,645

ACQUSTICAL DIAPHRAGM Filed Sept. 19, 1932 4 Sheets-Sheet l June 13,1933. w. c. sTL-:NGER

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1932 4 Sheets-Sheet 2,

l l i l l l June 13, `l1933. w. c. STENGER' 1,913,545

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1932 lLSheets--Sheelz 3 June 13,1933. w. c. sTENGx-:R 1313.645

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1952 4 Shees-Sheet 4 lIn-l s Raficof the Radius of the Arch fo the Rads of the rc n .zo .as .as HlTfudeof' the Arc Qn Percentage of the `'qrea lo? Base Patented June 13, 1933WILLEBALD CONRAD STENGER, OF CHICAGO, ILLINOIS l ACOUSTICAL DIAPHRAGMApplication. filed September 19, 1932.

This invention relates to the sounding elements in musical instruments,such as sound reproducing diaphragms of radio receivers, telephonereceivers, or the thin sounding boards of playing instruments and thediaphragms of transmitters.

The objects of the invention are mainly to obtain more brilliance oftone, distinctness and faithful reproduction of transmitted sounds,although coming from instruments of widely different character, and torender diaphragms less persistent in vibrating at some unimpressed rateand producing undesirable overtones. A further purpose of the inventionis to provide a sounding element of this class capable of vibrating as awhole but having a plurality of separate vibrating surfaces of differentcharacteristics, and with arbitrarily arranged nodal lines separating 0such surfaces whereby each of the surfaces becomes responsive tovibratory motions of distinctive character.

Other purposes of the invent-ion are to utilizel beneficial discoverieswith reference to the Vform of diaphragms resulting from eX- perimentalwork to find the most favorable arching of the sounding surfaces of thediaphragm, and point of application of vibratory movements transmittedto the diahragm. With such purposes in view a new ormulae is providedfor the construction of diaphragms.

The objects are accomplished by constructions as illustrated in thedrawings, wherein:

Figure 1 is a plan of a diaphragm to illustrate that the center ofapplication of energy for vibrating the diaphragm is definitely oil'-set from the geometric center thereof.

Figs. 2, 3 and 4 are edge views of the diam phragm illustrated by Fig.1, showing that it may be either flat or more or less arcuate, for thepurpose of adding rigidity to the diaphragm with reference to itsweight.

Fig. 5 is a plan view of a conical diam phragm constructed according tothis invention and showing a connection for receiving or transmittingmotion to the diaphragm, which connection marks the acoustical centeroffset from the geometrical center of the diaphragm.

Serial No. 633,818.

Fig. 6 is a side view of the diaphragm shown in Fig. 5, illustrating byfull lines with reference to broken lines, the change effected by0H-centering the connection.

Fig. 7 is a fragmentary section taken on 55 the line 7-7 of Fig. 5.

Fig. 8 is a plan view of a multi-wall or pyramidal form of diaphragm,providing a plurality of vibrating surfaces, and including improvementsillustrated by the preceding figures.

Fig. 9 is an end view of the diaphragm shown in Fig. 8.

Fig. 10 is an edge view of the wide side of the diaphragm.

Fig. 11 is an enlarged sectional detail taken on the line 11--11 of Fig.8.

Fig. 12 is a plan view of a pyramidal form of the diaphragm, includingthe peripheral supporting therefor, and corner reinforcements.

Fig. 13 is a sectional view taken on the line 13--13 of Fig. 12,illustrating both the peripheral and central supports of the diaphragm.

Fig. 14 is a sectional detail taken on the line 14-14 of Fig. 13.

Fig. 15 is a sectional detail taken on the line 15-15 of Fig. 12.

n Fig. 16 is a fragmentary face view showlng one cornerof the diaphragmillustrated by Figs. 12 and 13.

Fig. 17 is a sectional view taken on the line 17-17 of Fig. 16. 85

Fig. 18 is a sectional view similar to that shown by Fig. 17, but showsa more thin and flexible peripheral support.

Fig. 19 is an enlarged sectional detail to show one manner of supportingthe diaphragm near its center.

Fig. 20 illustrates in section another preferred mounting ofthe centralpart ofthe diaphragm.

Fig. 21 is a plan view of the supporting element for the center of thediaphragm.

Fig. 22 is a sectional detail taken on the line 22-22 of Fig. 9.

Fig. 23 shows in plan a center supporting ele: #ent for the diaphragmsuch as illustrated in Fig. 19, and indicates by dotted lines Where thefolds are made in this element.

Fig. 24 is a diagram showing the extent to which the side walls of thediaphragm are arched.

#Fig 25 is a graph for use in finding the correct center for arching thediaphragms.

The construction to which this invention relates has been developed fromexperiments with diaphragms of various forms, materials and mountingstherefor, and in this experimental work it appeared that diaphragmsarranged to receive vibratory motions through mechanical connections ora coil, which are located at the geometrical center, or which impressedthe vibratory motions in some manner to the diaphragm at its truecenter, that an undesirable interference occurred in the responsivediaphragm to the impressed vibrations. Objectionable overtone effectsand discordant intervals of musical sounds and of the voice seemed to becaused by the natural dominant tone of the diaphragm, or by effect orresults of oscillatory movements between two or more intervals. It wasfound that by changes in the construction here described, the diaphragmswould function with greater fidelity and clarity. These changes aremainly the fixing of an acoustical center which does not coincide withthe geometrical center of the diaphragm, and a slight arching of thediaphragm.

An example of the diaphragm thus ccnstructed would be a paper sheet,pressed while wet and under heat into a pyramid having a rectangularbase. The side walls slant at varying degrees. The four surfaces of thediaphragm are separated by nodal lines resulting from a crease in thepaper, or other material of which the diaphragm may be formed, at theedges of the meeting surfaces. Each of the surfaces is arched, thefunction of which arch is to afford greater uniformity in strength andresistance, and to give more stability to the vibratory movement of thediaphragm. This rectangular and pyramidal form of diaphragm may betruncated and provided with a collar at the apex for carrying themovable coil of the dynamic type of speaker. The height of the pyramidis determined according to the tensile strength and relation to thespecific gravity of the material used.

In the drawings, Figure l shows a diaphragm l, circular in outline, withits een ter at 2. According to this invention, should this diaphragm beused for example in a radio receiver, motion would be transmitted anddelivered to the diaphragm at the point 3, marked the acoustical center.The distance which this center is offset from the center 2 is found bytaking the square root of the area of the diaphragm and dividing it by84. In the form shown by Fig. 5, the area of the base 4 of the cone,divided by 84 gives the extent of offset of the acoustical center 5.

Figures 3 and 4: illustrate arcuate diaphragme having less altitude thanthe one shown by Fig. 6, as these diaphragms may be made of more rigidmaterial and thus require less altitude than the lighter` diaphragmillustrated by Fig. 6. In Fig. 6, the conical form of diaphragm is showntruncated for convenience in attaching the pin 6, which transmitsvibratory movements to the diaphragm.

Experience has proved that in pyramidal forms of sounding bodies thereis a very definite relation between the area of a sounding body, theheight or altitude of the pyramid and the proper arch for the walls ofthe sounding body. The radius of arch is found by multiplying the radiusof arc by a factor. The factor equals one plus sixteen times thealtitude of the pyramid divided by the square root of the area of thebase.

In the case of rectangular diaphragme the length of the base of the sidewall is equivalent to and is used instead of the square root of the areaof the base.

As an illustrative example assume that the area of the base is 625. Thesquare root of the length of an equivalent side is twentyfive. Assumethat the altitude is 12.5. Then the altitude is fifty percent of thelength of the side of the base. Fifty percent of sixteen is eight. Eightplus one equals nine. Hence, nine is the factor or the ratio of theradius of the arch to the radius of the arc.

In a similar manner if a side has a base line of thirty-six and thealtitude is nine, the percentage is twenty-tive. Twenty-five percent ofsixteen is four; add one, equals five. Hence the factor five. The factorfor all altitude ratios up to fifty percent is graphically shown in Fig.25.

The concavity of the diaphragms, 3 and 4, is increased by such an archor curvature imparted thereto from the center to the periphery. Thiscurving or arching of the diaphragm is better illustrated by the oneshown in Fig. l0, where the broken lines 7 indicate the straight sidesof a cone or pyramid,`whereas, the full lines 8 indicate the extent ofarching imparted to the diaphragm surfaces according to thisspecification. i

The arch consistent with the best results has a radius which may also bedetermined by the altitude of the cone or pyramid in percentage of thesquare root of the base of such cone or pyramid, multiplied by factorwhich may be found by reference to graph Q5. For example, if thealtitude is l0 percent of the square root of the area of the base, theratio of the radius of the arch, with reference to the radius of the arcpassing through points 9, l0 and 1l, Fig. 10, would be two andsix-tenths times. Fig. 24, the center for the arc is indicated atReferring to 12, or 12, and the center of the arch is indicated at 13and 13', in the two examples illustrated by this figure.

The diaphragm illustrated by Figs. 8 t0 11 inclusive is rectangular inoutline pressed to pyramidal form of unequal sides and calculated as toall its dimensions on the basis of the factor found by taking the squareroot of the area of its base. The altitude or distance between the baseof the pyramid and its apex is dependent upon the nature of the materialforming the diaphragm. Rigidity is added by increasing the altitude. Theside walls 14 and 15 extend upwardly at the same angle.

The acoustic center 16 is the normal distance to one side of thegeometrical center 17. The side walls 18 and 19 do not slant at the sameangle.

The diaphragm may be mounted at its periphery on a chassis 20, Fig. 11,through a flexible rectangular frame 21 attached to the inwardly bentbase flange 22. Diaphragm surfacing coatings 23 and 24 are sometimesemployed when necessary to render the material of the diaphragmimpervious to moisture.

The diaphragm illustrated by Figs. 12 to 18 inclusive is similar ingeneral form to that illustrated by Fig. 8 but with some variations, thecenter collar-shaped reinforcement 2G being cylindrical to support themovable' coil of a dynamic speaker, and the marginal bends 27 beingdoubled back on themselves to increase resilience in the marginalsupport of the diaphragm.

The marginal corners of the diaphragm are split in this instance andreinforced by a light leather strip 28. Centrally the diaphragm issupported on the chassis 29 through a resilient connection 30 such asillustrated by Fig. 21, which is a development of this supporting memberwith the lines upon which it is creased indicated at 31. The centralsupport may be formed of paper. Fig. 23 illustrates a variation 32 ofthis supporting means for use in connection with electromagneticspeakers having armatures indirectly connected with the diaphragm.

The large sectional views 19 and 20 indicate the movable coil 33attached to collar 26. In one case the support 30 is secured to the faceor delivery side of the diaphragm and to the pole of the magnet by screw34. In Fig. 20

'- the resilient support 30 is secured to the rear face of the diaphragmand to the chassis 29.

Referring to Figs. 8 and 12 where the four sides of the diaphragms meetrespectively on the lines 35 and 36 the crease adds rigidity along suchlines and around which the separate walls of the diaphragm may hinge inindependent oscillatory movements.

Thus while the diaphragm is vibrating as a whole, independent vibrationsoccur in the separate walls thereof. Vhile this diaphragm may vibratewith the same amplitude throughout, waves on its separate surfaces areof less amplitude toward the center than near the periphery. This is dueto its form, the more rigid valleys 35 and 36 radiating from the center.

For best results with the pyramidal form of diaphragm with a rectangularbase illustrated by Figs. 8 and 12 it is found that the dimensions ofthe base should be unequal, with substantially the following proportionsbased on the square root of the area of the base. The long dimension isfour-thirds of the square root of the base. and the short dimension isthree-fourths of the square root of the base. f

In using the invention these peculiar characteristics as to dimensionsand form are followed whether the diaphragm is used for the directreception and transmission of sound waves or the reproduction of soundwhen the waves are mechanically or electromagnetically imparted to thediaphragm or in a musical instrument such as the sounding board of apiano.

I claim:

1. In an acoustic instrument, a sounding element of pyramidal shape, anarch in said sounding element based on altiude, divided by the squareroot of the area of the base.

2. In an acoustic instrument, a p; amidal sounding element having arectangu.V .r base, arches in the side walls of said element, the radiiof said arches being a function of the altitude of the pyramid dividedby the base of the side wall.

3. In a musical instrument a sound wall, an arch in said sound wall, afactor for the radius of said arch equal to one plus sixteen times thealtitude divided by the Asquare root of the area of the base. f

4. A diaphragm for sound instruments in combination with means forimparting vibratory motions to the diaphragm and an operative connectionbetwee the diaphragm and said means which is attached to the diaphragmto one side of the geometrical center of the diaphragm the distance ofapproximately one eighty-fourth of the square root of the area of thediaphragm.

5. A diaphragm for sound instruments of conical form and means forvibrating the diaphragm mounted thereon in offset relation with thegecmerical center of the diaphragm an extent equal to substantially oneeightyfourth of the square root of the area of the base of the coneformed by the diaphragm.

6. A sounding element having a pyrainidal shape, and means co nectedwith said element for imparting vibratory motions thereto, theconnection between said means and the sounding element being offset fromthe geometrical center of the sounding element a disf.' anceapproximating one eighty-fourth of the square o the area of the base ofthe pyramid formed by said element.

7. A diaphragm for sound instruments having a plurality of sidesinclined toward a common apex, located substantially one eighty-fourthof the square root of the base oi' the diaphragm to one side of thegeometrical center of the diaphragm.

8. A diaphragm for sound instruments supported at its periphery by areversely folded peripheral extension of the diaphragm, and means forsupporting the center of the diaphragm comprising a reversely foldedresilient member.

9. A diaphragm for sound instruments supported at its periphery by areversely folded peripheral extension of the diaphragm, means forsupporting the center of the diaphragm comprising a reversely foldedresilient member, and means attached to the diaphragm for impartingvibratory motions to the diaphragm, said means being disposed with itsaxis spaced to one side of the geometrical center of the diaphragm adistance equal to one eighty-fourth of the square root ot the area ofthe base ot the diaphragm.

l0. A diaphragm for acoustic instruments having an operative cent-ralconnect-ion Which is located substantially one eightyi`ourth of thesquare root of the area of the diaphragm to one side ot the geometricalcenter of the diaphragm, said diaphragm being arched, the radius ofwhich arch is based on altitude divided by the square root of the areaof the diaphragm.

ll. An acoustical diaphragm of pyramidal torni having a rectangularbase, the dimensions ot said base being unequal, the long side having avalue Which is four-thirds of the square root of the base, and theshorter side having al length which is substantially three-fourths ofthe square root of lthe base.

Signed at Chicago in the county of Cook and State of Illinois this 25thday of August 1932.

VILLEBALD CONRAD STENGER.

